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C5 RS6 MAF design fault

IchBautAuto

New member
Not a really active forum here but I have some info for RS6 owners. While I was sorting out some issues with MAF seals it became apparent that the MAF design was flawed in this application. I took a swag of measurements and they have been confirmed by gregstv on here and some UK folk. Initially I had some concern that the wrong MAF may have been installed when I bought the car but that isn't so.

Long time owners will be only too aware that any time the whole airbox is removed, there is every chance that on replacement, either fault codes or a CEL will appear. This is said to be an issue, whether done at home or even by AUDI mechanics.

The answer is that the MAF body is some 15-17mm too short. The outcome when the MAF is secured to the airbox in the OEM configuration is that the MAF just enters the manifold seals rather than fully seats and any misalignment at all can mean that a seal is not made and a fault is generated. If there is any airbox issues in refitting such as wiring loom obstructions under the box then the MAF may not even enter the seal at all.

I have put together a home brew fix to check it out and depending on the outcome, I'll post up dimensions for the fix. It would be nice to have a machined component and I may well do that but it isn't the sort of fix that would be economical to manufacture in very small numbers.
 
Dedication or exasperation? You'd think that they would get something as basic as this right in a quarter Mil car. Anyway, feels good to have put the finger on the issue and I'll get mine fixed toot sweet so one less thing to bang the head over.
 
Not a really active forum here but I have some info for RS6 owners. While I was sorting out some issues with MAF seals it became apparent that the MAF design was flawed in this application. I took a swag of measurements and they have been confirmed by gregstv on here and some UK folk. Initially I had some concern that the wrong MAF may have been installed when I bought the car but that isn't so.

Long time owners will be only too aware that any time the whole airbox is removed, there is every chance that on replacement, either fault codes or a CEL will appear. This is said to be an issue, whether done at home or even by AUDI mechanics.

The answer is that the MAF body is some 15-17mm too short. The outcome when the MAF is secured to the airbox in the OEM configuration is that the MAF just enters the manifold seals rather than fully seats and any misalignment at all can mean that a seal is not made and a fault is generated. If there is any airbox issues in refitting such as wiring loom obstructions under the box then the MAF may not even enter the seal at all.

I have put together a home brew fix to check it out and depending on the outcome, I'll post up dimensions for the fix. It would be nice to have a machined component and I may well do that but it isn't the sort of fix that would be economical to manufacture in very small numbers.


Instead of machining what about 3D printing, the only real time is drawing the 3D model. Printing with PETG is robust and not affected by oil or temperature.

Happy to assist I have a commercial grade printer.
 
Interesting I never had fitment issues with my original MAFs, I’m saying that I’m about 3 MAF models past that


Sent from my iPhone using Tapatalk
 
Instead of machining what about 3D printing, the only real time is drawing the 3D model. Printing with PETG is robust and not affected by oil or temperature.

Happy to assist I have a commercial grade printer.

I'm really without much knowledge on 3D printing, I would have expected the model to have some heat restrictions due to my understanding of how it worked so I didn't go any further down that track. That said, I have my solution, just waiting on the silicone hose to arrive in the post to complete. If that is an option then I'll discuss with you on the best way ahead. It is simple and has no real tension, torsion or compression components, just two spacers subject to engine bay heat.

MAF pre spacer.jpg

This is my airbox with the MAF's fully inserted into the manifold, you can see there is a 15mm gap between the intake horn and the MAF, which shouldn't exist.

MAF seated.jpg
The fix is a 15mm spacer that sits above the MAF and below the bottom of the air horn to both hold the MAF down in place and smooth the airflow into the MAF. There is a second 15mm spacer that is flanged and attaches to the bottom of the airbox to provide an additional air seal between the MAF and Airbox. I'll flick you the thumbnail drawings by email, I think I have it somewhere.
 
Interesting I never had fitment issues with my original MAFs, I’m saying that I’m about 3 MAF models past that


Sent from my iPhone using Tapatalk

One of those issues where you would not expect anyone to really notice it as the MAF is fixed to the airbox from the factory, so looks fine from above, correctly seated in the intake horn and if installed with care, engages with the seal in the manifold and doesn't throw a CEL or fault. The bit that is hard to see is the MAF only just engages with the manifold seal. Impossible for it to go in further as it is secured by the airbox. I put up some thumbnail drawings on 246 with the measurements and they have been confirmed by others.

I ended up here as I wanted to be able to remove the airbox without removing the MAF's. Did all the measurements without the MAF in place and this was the outcome. I am using Apikol seals and I noticed yesterday when I fitted the MAF's back in place that they were a slip fit for the first 5mm and then the last 15mm into the manifold was a very stiff push. The MAF housing is slightly stepped at both ends to facilitate engagement with the seals at each end so this was to be expected. For those guys that are sticking with the standard airbox, hopefully this will make their lives easier as the UK guys report a fair bit of trouble with getting the seal right at times.
 
The trial solution. two pairs of spacer made from silicone hose, 70mm ID and 80mm ID.
spacers.jpg

One set placed over the MAF and under the airbox
maf spacers.jpg

The second set inserted into the airbox above the MAF.
without.jpg
These weren't perfect, the hose ID is 70mm and the air horn is 72mm so a pair of egg rings were exactly the right size to match the ID of the sir horn and provide an alloy surface for the intake air
egg rings.jpg

Basically, the idea has been to extend the length of the MAF body so that the MAF is fully inserted into the manifold and also seals against the air horn in the airbox. The trial was a roaring success and now with the offer from Tas_Audi to try and 3D print a pair, we'll see if something of the standard to match the rest of the car can be produced.
 
Time passes. I had a very generous offer from a forum member to 3D print up some spacers to my design and they arrived today. Perfect fit and they enable the C5 RS6 owner to rectify the factory error of excessive clearance between the manifold, MAF and airbox. They are able to be used to maintain the original factory configuration of the MAF bolted to the airbox (terrible concept in my opinion) or to make the airbox removable without moving the MAF's and damaging the wiring.

If you own a C5 RS6 with the standard airbox then this or something similar should be needed to put this problem to bed for good.

MAF spacers lores.jpg
 
Time passes. I had a very generous offer from a forum member to 3D print up some spacers to my design and they arrived today. Perfect fit and they enable the C5 RS6 owner to rectify the factory error of excessive clearance between the manifold, MAF and airbox. They are able to be used to maintain the original factory configuration of the MAF bolted to the airbox (terrible concept in my opinion) or to make the airbox removable without moving the MAF's and damaging the wiring.

If you own a C5 RS6 with the standard airbox then this or something similar should be needed to put this problem to bed for good.

View attachment 31646

That's a nice neat fix. Nothing worse than chasing air leaks.
 
Incredible when the factory drawings clearly show (and specify) the MAF sitting tightly between the airbox and the manifold. Reality is that the MAF is 15-17mm shorter than it should be and because the MAF is secured to the airbox, the numerous air leaks that people get are all between the MAF and the manifold as the MAF just enters the manifold seal in the best case or not in others. Fault codes, bit of crap into the manifold etc are commonly reported around the world and it's more difficult to detect the cause than it would appear. Inspection mirrors and endoscopes are useful.
 
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